Air quality index: what each band means
The US AQI runs from 0 to 500 across six bands. The Canadian AQHI runs from 1 to over 10 and is built from relative mortality risk.
Preliminary readings from official networks, not fully validated. For health decisions follow your doctor and your local environmental agency.
Index
| Range | What to do |
|---|---|
| Good (0 to 50) | No health risk expected. |
| Moderate (51 to 100) | Unusually sensitive people may cut back on outdoor effort. |
| Unhealthy for sensitive groups (101 to 150) | Children, older adults and people with asthma or heart disease should reduce hard outdoor activity. |
| Unhealthy (151 to 200) | Everyone may feel effects; sensitive groups should stay indoors. |
| Very unhealthy (201 to 300) | Health alert: avoid outdoor exertion. |
| Hazardous (above 300) | Emergency conditions: stay in filtered air. |
AQHI
| Range | What to do |
|---|---|
| Low (1 to 3) | Normal outdoor activity. |
| Moderate (4 to 6) | People with symptoms may ease off outdoors. |
| High (7 to 10) | Sensitive groups should reduce or reschedule outdoor activity. |
| Very high (above 10) | Everyone should reduce outdoor exertion. |
PM2,5 → AQI
| PM2,5 (µg/m³) | AQI | Category |
|---|---|---|
| 5.0 | 28 | Good (0 to 50) |
| 9.0 | 50 | Good (0 to 50) |
| 20.0 | 71 | Moderate (51 to 100) |
| 35.4 | 100 | Moderate (51 to 100) |
| 55.4 | 150 | Unhealthy for sensitive groups (101 to 150) |
| 100.0 | 182 | Unhealthy (151 to 200) |
| 150.0 | 225 | Very unhealthy (201 to 300) |
| 250.0 | 350 | Hazardous (above 300) |
- U.S. EPA AirNow (áreas de referência, arquivo público)Licence: Dado público da EPA, sujeito às AirNow Data Use Guidelines (atribuição obrigatória) · Credit: U.S. EPA AirNow e a agência estadual, tribal ou local que fez a mediçãoDados preliminares, sem validação final; não servem para fins regulatórios.
- Environment and Climate Change Canada — AQHILicence: ECCC End-use Licence (uso livre com citação da fonte) · Credit: Environment and Climate Change Canada
How to read these numbers
The AQI is computed separately for each pollutant from breakpoints set by the EPA, and the index of the moment is the highest of them. The PM2.5 breakpoint was tightened in 2024: 9 µg/m³ as a 24 hour average now marks the end of the good band.
The Canadian index works differently: it combines ozone, nitrogen dioxide and PM2.5 into a health risk formula, so there is no exact conversion between AQHI and AQI.
Frequently asked questions
- Is AQI 100 bad?
- It is the top of the moderate band. It means the concentration has reached the national air quality standard; people with asthma or heart disease may already notice it.
- How do I turn µg/m³ into AQI?
- By linear interpolation inside the pollutant band. This page shows the breakpoint table used in the calculation.